Re: [PATCH v12 5/9] nvme: add copy offload support

[Nitesh Shetty]

On 23/06/08 09:24PM, Christoph Hellwig wrote:
> On Thu, Jun 08, 2023 at 05:38:17PM +0530, Nitesh Shetty wrote:
> > Sure, we can do away with subsys and realign more on single namespace copy.
> > We are planning to use token to store source info, such as src sector,
> > len and namespace. Something like below,
> >
> > struct nvme_copy_token {
> > 	struct nvme_ns *ns; // to make sure we are copying within same namespace
> > /* store source info during *IN operation, will be used by *OUT operation */
> > 	sector_t src_sector;
> > 	sector_t sectors;
> > };
> > Do you have any better way to handle this in mind ?
>
> In general every time we tried to come up with a request payload that is
> not just data passed to the device it has been a nightmare.
>
> So my gut feeling would be that bi_sector and bi_iter.bi_size are the
> ranges, with multiple bios being allowed to form the input data, similar
> to how we implement discard merging.
>
> The interesting part is how we'd match up these bios.  One idea would
> be that since copy by definition doesn't need integrity data we just
> add a copy_id that unions it, and use a simple per-gendisk copy I/D
> allocator, but I'm not entirely sure how well that interacts stacking
> drivers.

V13[1] implements that route. Please see if that matches with what you had
in mind?

[1] https://lore.kernel.org/linux-nvme/20230627183629.26571-1-nj.shetty@xxxxxxxxxxx/

Thank you, 
Nitesh Shetty